This invention relates to pickup arm drive devices, and more particularly to a pickup arm drive device of a record player provided with an automatic music selection device which automatically selects a desired piece of music during the playing of a record disc on the surface of which a plurality of pieces of music have been recorded.
A record player provided with such an automatic music selection device has been designed in the following fashion. A pickup cartridge with an inter-music sensor including a light source and a light receiving element is moved along the record disc so that an inter-music space is detected from the variation of the output of the inter-music sensor. The output of the inter-music sensor corresponds to the variation in intensity of light which is reflected from the surface of the record disc and is received by the light receiving element. When the number of inter-music spaces thus detected becomes equal to an address of the desired piece of music which has been externally specified, the pickup cartridge is stopped and then the pickup cartridge is lowered onto the record disc to play (reproduce) the latter. However, the pickup cartridge tends to move beyond a position where it should be stopped due to the mass of the arm or the characteristic of the drive section. That is, a so-called "over-shoot" phenomenon occurs. This stop position error due to the "over-shoot" phenomenon is minimized by driving the pickup arm in the opposite direction immediately when the pickup arm is stopped.
While the inter-music spaces are detected, the record is being turned. Therefore, if the record is eccentric or warped, the stylus of the pickup cartridge which is positioned right above the detected inter-music space may not be lowered onto the inter-music space. That is, the pickup cartridge might be displaced inwardly or outwardly relative to the inter-music space. If such a displacement occurs, the record is played from the end portion of the preceding piece of music or the middle portion of the desired piece of music. Thus, the conventional automatic music selection device has no suitable countermeasure against the eccentricity of the record disc. Theoretically, if the eccentricity is larger than the width of the inter-music space, it is impossible to correctly lower the pickup cartridge onto the aimed inter-music space.
In the case where a plurality of pieces of music preselected and programmed are automatically played in the programmed order, i.e., in the case where a record is played in a so-called "random music selection mode", it is necessary to detect the inter-music spaces while the record is being played (or traced). However, since the inter-music sensor is in proximity to the record surface during the record playing operation, the difference between the amount of light received from the modulated groove zone and the amount of light received from the inter-music space is much smaller than the difference during the "lead-in" operation or the "return" operation. This is due to the fact that the amount of light received from the modulated groove zone of the record increases during the record playing operation. Therefore, with the arrangement that an inter-music space is detected by using the output of a single inter-music sensor, it is considerably difficult to set the threshold level and accordingly the detection result is liable to be erroneous.
Furthermore, there is a record player provided with a muting circuit for muting a pickup output. The muting circuit is provided to suppress noise such as for instance an impact sound which is produced when the stylus of the pickup cartridge is lowered onto the record. The muting circuit is typically designed so that the muting control is released with the timing that after the stylus of the pickup cartridge has been lowered onto the record, the output of the single inter-music sensor provided in proximity to the stylus exceeds a threshold level corresponding, for instance, to a substantially central position on the inter-music space. However, with the arrangement that an inter-music space is detected by utilizing the output of a single inter-music sensor, it is considerably difficult to set a threshold level corresponding to a desired inter-music position, and accordingly erroneous operations are liable to occur. In addition, when the stylus lowering position is displaced, for instance, radially inwardly of the record due to the eccentricity of the record, the muting control cannot be released.